Magic Block Piercing Trick

Hocus Pocus! You present your audience with six colored blocks, each one with a hole through its face. Your audience inspects the blocks as well as the box you will place them in and the pin you will pierce them with. A volunteer selects two of the six blocks. After placing all six blocks into the box, you pierce the box and all the blocks with a pin. Waving your hand over the box, you say a magic word. Turning the box upside down, the lid falls off and out drops the two chosen blocks! Bu